The present invention relates to display apparatus having selectable communication protocol for use in a personal computer system.
A personal computer system typically comprises a computer system unit having: a memory, including a mass storage device such as a hard disk drive, for storing data and computer program instructions; and, a microprocessor for manipulating the data stored in the memory according to the instructions of the computer program. User input means comprising a keyboard and pointing device such as a mouse are connected to the system unit to permit a user to control execution of program code by the system unit. Display apparatus, such as a cathode ray tube display, liquid crystal display panel, or the like, is connected to the system unit to display data manipulated by the system unit to the user. The program code typically comprises application software such as a word-processor and operating system software for managing execution of the application software by the system unit. Device driver software configures the system unit to communicate data between the application software and peripheral devices such as the display apparatus. Operating system and application software products are typically supplied with a range of device drivers from which a user selects the appropriate driver for a particular personal computer configuration. However, there is now such a wide range of display devices available for connection to personal computer system units that it can be difficult to select the appropriate device driver for a particular display. If the correct device driver is not loaded, the performance of the display will not be optimised. In particular, if parameters specific to the display device, such as maximum refresh rate, are not set to the right value in the system unit, objectionable front of screen performance, such as flicker, may result in the display device.
With a view to solving the above problem, the Video Electronics Standards Association (VESA) has produced a communication protocol standard for a Display Data Channel (DDC). DDC establishes a serial communication link between the display device and the system unit of a personal computer system. The link enables the system unit to read a data file containing Extended Display Identification Data (EDID) from the display device. The EDID describes the operational capabilities of the display device DDC thus enables the system unit to load the optimum device drivers for the display device without any user intervention. DDC is designed around a 15 pin xe2x80x9cD shellxe2x80x9d connector. This type of connector is generally used by the PC industry to connect the display device to a video adaptor of the system unit. There are three types of DDC specified: DDC1;
DDC2B; and DDC2AB. In DDC1, the system can only read the EDID from the display device. In DDC2B and DDC2AB can both read data from and write data to the display device. DDC2B and DDC2AB use signal lines in the connector which were used to provide identification (ID) bits 1 and 3 from the display device to the video adaptor in previous identification schemes. DDC1 uses only the line previously assigned to ID bit 1. The identification bits allowed previous system units (such as the IBM PS/2 range of system units) to recognise which type of display device is attached and hence decide which video modes were supported. This was a simple and inferior attempt to provide the function now offered by DDC. The line previously used for ID 1 is assigned by DDC1, DDC2B, and DDC2AB to carry data from the display device to the system unit. The line previously used for ID 3 is assigned by the DDC2B and DDC2AB to carry a clock signal between display device and the system unit to permit two-way communication of data between the display device and the system unit. It will thus be appreciated that, in a personal computer configuration comprising an older system unit and a DDC compatible display device, the device will produce either a xe2x80x9c0xe2x80x9d or a xe2x80x9c1xe2x80x9d on the line previously used for ID1, depending on the piece of DDC data the display device is transmitting at the time that the older system unit checks the ID bits in accordance with it""s initialisation program. Assuming that ID bits 0 and 2 (which are not used by DDC) are grounded inside the connector shell, the older system unit would see ID bits of either xe2x80x9c1010xe2x80x9d, or xe2x80x9c1000xe2x80x9d. xe2x80x9c1010xe2x80x9d would be acceptable as this is an industry standard monitor ID bit pattern. However, xe2x80x9c1000xe2x80x9d is undefined as far as the older system unit is concerned, possibly leading to the system unit flagging a configuration error. Furthermore, the older system unit may see different ID bits at each boot up, thereby misleading the system unit into believing the that the display device has been changed. Again, a configuration error may result.
One known solution to the above problem is to introduce a mechanical two-position switch to the display device, with one switch position indicating DDC operation and the other position indicating ID bit operation. This solution has the disadvantages of increasing both product cost and physical complexity.
Another known solution is to introduce bi-directional FETs to the display device to make the critical ID bit lines (bits 1 and 3) go open circuit if ID bit mode is required. This solution is, again, complex and expensive to implement.
A further solution is to fit a dongle in series between the video adaptor of the older system unit and the display device. However, this solution is also expensive to implement.
In accordance with the present invention, there is now provided display apparatus comprising: a display screen; display drive means for generating a picture on the display screen in response to picture information from an external video source releasably connectable to the display apparatus; user control means for adjusting the picture generated by the display drive means in response to a manual input; and selection means for selecting, in response to a configuration code input via the user control means, one of a plurality of sets of control data for communication to the video source.
This advantageously permits the display to be selectively configured, via the user controls, to communicate with a computer system unit in accordance with any one of a plurality of communication protocols, such as DDC, DDC2B, DDC2AB, or conventional ID bit protocols, for example.
Preferably, the selection means comprises memory means for storing the sets of control data. The memory means preferably comprises a nonvolatile memory for storing at least one of the sets of control data.
In a preferred embodiment of the present invention, said one set of control data stored in the non-volatile memory comprises Extended Display Identification Data file for sequential communication to the video source.
At least of the sets of control data preferably comprises an N bit identification word for parallel presentation to the video source.
Preferably, the plurality of sets of control codes comprises a first set of control codes and a second set of control codes, wherein the selection means switches between the first set and the second set upon receipt of the configuration code.
The user control means preferably comprises a user control panel having a key pad including a plurality of manually actuable buttons. In one preferred embodiment of the present invention, the configuration code is supplied to the selection means in response to simultaneous depression of a plurality of the buttons. In another preferred embodiment of the present invention, the configuration code is supplied to the selection means in response to depression of a plurality of the buttons in a predefined sequence. In yet another preferred embodiment of the present invention, the configuration code is supplied to the selection means in response to depression of one of the buttons for a predefined period of time (15 seconds, for example). In a further embodiment of the present invention, the user control panel comprises a button dedicated to supplying the configuration code. In a particularly preferred embodiment of the present invention, the configuration code is preferably supplied to the selection means in response to simultaneous depression of two of the buttons.
In a particular preferred embodiment of the present invention to be described shortly, the display screen comprises a cathode ray tube display screen.
It will be appreciated that the present invention extends to a computer system comprising: computer memory means for storing a computer program instructions and data; processor means for executing the computer program instructions to manipulate the data; user input means for controlling execution of the program instructions by the processor means; a video source for generating picture information corresponding to data manipulated by the processor means; and display apparatus as described the above paragraphs for displaying a picture in response to picture information received from the video source.
A preferred embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:
FIG. 1 is a block diagram of a personal computer system; and
FIG. 2 is a block diagram of display apparatus of the present invention.